Much like amazon reviews they absolutely cannot be trusted to be a representation of the truth
This is a suitable problem to be solved by decentralised system.
That would also be open to abuse. It's difficult to stop dishonest PR firms (or anyone else) from flooding positive or negative comments.
Does anyone have any ideas how to solve this?
If you are happy to pay for this, then there are a variety of options with a sliding cost/usefulness/accuracy scale.
If you are looking for reliable, accurate, balanced reviews conducted by anonymous ethical independent agents, and you don’t think consumers of that information should pay for it, then I believe the answer is there is no perfect solution that satisfies all those constraints simultaneously.
Depressingly is also means the most shady companies that will abuse systems like this, will also seem to have a sparkling reputation - actually harming customers if they rely on these sites.